Nuclear gauges and methods of configuration and calibration of nuclear gauges

ABSTRACT

A method for calibrating a nuclear gauge of the having a source includes providing a nuclear gauge comprising a radiation source, the radiation source being coupled with a computing system with a machine readable program stored thereon containing a calibration routine. An operator places the gauge on one or more specified blocks to adjust the source within each block to one or more specified positions to initiate a count. The method includes determining that the source is at each position before each count begins, adjusting the counting times before each count begins by the program on the nuclear gauge based on each position of the source to obtain calibration information, obtaining counts at each position, storing the counts within the computing system of the nuclear gauge, and calculating for each position calibration coefficients.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/477,405 filed on Apr. 3, 2017 and to issue as U.S. Pat. No.9,958,562, which is a continuation of U.S. patent application Ser. No.14/748,171 filed on Jun. 23, 2015, to issue as U.S. Pat. No. 9,612,346on Apr. 4, 2017. U.S. patent application Ser. No. 14/748,171 is acontinuation of U.S. patent application Ser. No. 13/414,680 filed onMar. 7, 2012, to issue as U.S. Pat. No. 9,063,062 on Jun. 23, 2015. U.S.patent application Ser. No. 13/414,680 is a divisional application ofU.S. patent application Ser. No. 12/348,821 filed on Jan. 5, 2009, toissue as U.S. Pat. No. 8,164,048 on Apr. 24, 2012. This and eachabove-referenced patent application claims the benefit of priority ofU.S. Provisional Patent Application Ser. Nos. 61/010,022, 61/010,191 and61/010,103, all filed Jan. 4, 2008. Each above-referenced earlier-filedpatent application is incorporated herein in its entirety.

TECHNICAL FIELD

The present subject matter generally relates to an apparatus and methodfor determining the density and/or moisture of materials and, moreparticularly, relates to nuclear gauges used in measuring the densityand/or moisture of construction-related materials.

BACKGROUND

Nuclear radiation gauges have been widely used for measuring the densityand moisture of soil and asphaltic materials, or other constructionmaterial. As used herein, construction material is any materials used inbuilding roads or foundational structures including, but not limited tosoils, asphalts, asphalt-like materials, concrete, composite materials,or the like. Such gauges typically include a source of gamma radiationwhich directs gamma radiation into the test material, and a radiationdetector located adjacent to the surface of the test material fordetecting radiation scattered back to the surface. From this detectorreading, a determination of the moisture and density of the material canbe made.

These gauges are generally designed to operate either in a “backscatter”mode or in both a backscatter mode and direct transmission mode. Ingauges capable of direct transmission mode, the radiation source isvertically moveable from a backscatter position, where it resides withinthe gauge housing, to a series of direct transmission positions, whereit is inserted into small holes or bores in the test specimen.

Many of the gauges commonly in use for measuring density of soil,asphalt and other materials are most effective in measuring densities ofmaterials over depths of approximately 3-12 inches. However, with theincrease in cost of paving materials, the practice in maintaining andresurfacing paved roadbeds has become one of applying relatively thinlayers or overlays having a thickness of one to three inches. Withlayers of such a thickness range, many density gauges are ineffectivefor measuring the density of the overlay because the density readingobtained from such gauges reflects not only the density of the thinlayer, but also the density of the underlying base material.

Nuclear gauges capable of measuring the density of thin layers ofmaterials have been developed by Troxler Electronic Laboratories, Inc.of Research Triangle Park, North Carolina. For example, thin layerdensity gauges are disclosed in U.S. Pat. Nos. 4,525,854, 4,701,868,4,641,030, 6,310,936 and 6,442,232, all of which are incorporated hereinby reference in their entirety. Some of the gauges disclosed in theabove-referenced patents are referred to as “backscatter” gauges becausethe radiation source does not move outside the gauge housing, which isnecessary for measurement in the direct transmission mode. In some ofthe gauges disclosed in the above-referenced patents, the gauge can haveradiation sources that can also be extended outside of the gauge housingand into the material to be measured in a direct transmission mode.Typically, the source rods can extend up to about 12 inches.

As disclosed in the above patents, the preferred method of measuring thedensity of thin layers of materials, such as asphalt, is nondestructiveand uses the backscatter mode. One method requires two independentdensity measurement systems. The geometry of these two measurementsystems must be configured with respect to one another and with respectto the medium being measured in such a manner that they measure twodifferent volumes of material. The two different volumes are notmutually exclusive insofar as they partially overlap one another.Measurement accuracy depends upon a larger portion of the volumemeasured by one of the measurement systems being distributed at a lowerdepth beneath the gauge than the volume measured by the othermeasurement system. This is accomplished by placing one radiationdetection system in closer spatial proximity to the radiation sourcethan the other detection system. Another volume specific measurement istypically used in soils and requires drilling a small hole in thematerial under test. This method is referred to as the directtransmission mode

To determine the positioning of the source rod during use normallyincludes a visual inspection of the location of the source rod relativeto an index rod and/or the height of the portion of the source rodextending out of the gauge housing. Such determination can beproblematic and inaccurate. Contact strips whose resistance varies withposition have also been used to detect the length that the source rodhas moved. These strips often wear out.

Preparation for configuring a gauge can be time consuming. For gaugesused in the past, each type of gauge would be configured differently sothat there would be multiple configuration programs for gauges. Thus,each type of gauge could have a separate configuration program writtenfor it.

Also, as known in the art, the calibration of a nuclear gauge, forexample, a 12-position nuclear gauge is time consuming, and many qualitycontrol checks have to be implemented. For instance, programs over theyears have been developed that analyze the calibration curves to findstatistical variations in the gauge. For example, the typicalcalibration constants, count rate, precision and slope as a function ofdensity of each gauge, along with their standard deviations, have beendetermined. These parameters are an important part of the diagnostics ofthe health of a gauge. Currently, only at the factory can this sort ofdiagnostics be accomplished. In the factory, external computer networksare wired to each calibration bay, the data is transferred by wire fromthe instrument to the external computer, where computer programs knownin the art are used to curve fit, transfer the coefficients, store thecoefficients to the gauge, and quality control check each measurementfor deviations out of the standard expected values.

There remains a need in the art for a nuclear gauge capable of operatingin backscatter mode and/or direct transmission mode, and which issuitable for efficiently measuring the density and moisture ofconstruction material.

SUMMARY

In accordance with this disclosure, nuclear gauges for determining thedensity and/or moisture of materials and methods of configuration andcalibration of nuclear gauges are provided. It is, therefore, an objectof the present disclosure to provide nuclear gauges used in measuringthe density and/or moisture of construction-related materials andmethods for configuration of the gauges and methods of calibration ofthe gauges. This and other objects as may become apparent from thepresent disclosure are achieved, in whole or in part, by the subjectmatter described herein.

An object of the presently disclosed subject matter having been statedhereinabove, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident as thedescription proceeds when taken in connection with the accompanyingdrawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present subject matter includingthe best mode thereof to one of ordinary skill in the art is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures, in which:

FIG. 1 illustrates a perspective view of an embodiment of a nucleargauge according to the present subject matter;

FIG. 2 illustrates a vertical cross-sectional view of the nuclear gaugeillustrated in FIG. 1;

FIG. 3 illustrates a perspective view of a portion of the nuclear gaugeillustrated in FIG. 1;

FIG. 4A illustrates a perspective view of an embodiment of a supporttower, or source rod housing, used in a nuclear gauge according to thepresent subject matter;

FIG. 4B illustrates a horizontal cross-sectional view of the supporttower illustrated in FIG. 4A;

FIG. 5 illustrates a close-up perspective view of the support towerillustrated in FIG. 4A;

FIG. 6 illustrates a perspective view of the support tower illustratedin FIG. 4A;

FIG. 7A illustrates a perspective end view of the support towerillustrated in FIG. 4A;

FIG. 7B illustrates a perspective view of the support tower illustratedin FIG. 4A and an embodiment of a tube spacer to be inserted into thetower according to the present subject matter;

FIG. 7C illustrates a perspective view of an embodiment of a source rodbearing to be inserted into a support tower, or source rod housing,according to the present subject matter;

FIG. 8 illustrates a perspective view of an embodiment of a supporttower, or source rod housing, and base of a gauge housing according tothe present subject matter;

FIG. 9 illustrates a plan view of an embodiment of a depth strip thatcan provide a non-contact measurement in a nuclear gauge according tothe present subject matter;

FIG. 10 illustrates a perspective view of an embodiment of a supporttower, or source rod housing, and depth strip according to the presentsubject matter;

FIG. 11 illustrates a perspective end view of the support tower anddepth strip illustrated in FIG. 10;

FIG. 12 illustrates a perspective view of an embodiment of a supporttower and base of a gauge housing according to the present subjectmatter;

FIG. 13A illustrates an exploded view of an embodiment of a handle usedin a nuclear gauge according to the present subject matter;

FIG. 13B illustrates another exploded view of an embodiment of a handleused in a nuclear gauge according to the present subject matter;

FIG. 13C illustrates another exploded view of an embodiment of a handleused in a nuclear gauge according to the present subject matter;

FIG. 13D illustrates horizontal cross-sectional view of the handleillustrated in FIG. 13A;

FIG. 14 illustrates an exploded view of an embodiment of a source rodand handle according to the present subject matter;

FIG. 15 illustrates a perspective view of an embodiment of a source rodbeing inserted a support tower, or source rod housing, according to thepresent subject matter;

FIG. 16 illustrates a perspective view of an embodiment of a nucleargauge according to the present subject matter;

FIG. 17 illustrates a partially exploded bottom view of an embodiment ofa nuclear gauge according to the present subject matter;

FIG. 18A illustrates a perspective view of an embodiment of areplaceable sliding guide for use in a nuclear gauge according to thepresent subject matter;

FIG. 18B illustrates a plan view an embodiment of a replaceable slidingguide for use in a nuclear gauge according to the present subjectmatter;

FIG. 18C illustrates a side view of an embodiment of a replaceablesliding guide for use in a nuclear gauge according to the presentsubject matter;

FIGS. 19-24 illustrate partially perspective bottom views of anembodiment of a nuclear gauge and components of a radiation shieldassembly according to the present subject matter;

FIG. 25A illustrates a partial perspective view of an embodiment of anuclear gauge according to the present subject matter;

FIG. 25B illustrates a partial perspective view of an embodiment of anuclear gauge according to the present subject matter;

FIG. 25C illustrates a partial perspective view of an embodiment of anuclear gauge according to the present subject matter;

FIG. 26 illustrates a schematic view of an embodiment of a circuit thatcan be used in a nuclear gauge according to the present subject matter;

FIG. 27 illustrates a schematic view of an embodiment of a nuclear gaugein communication with a nuclear gauge configuration system according tothe present subject matter;

FIG. 28 illustrates a flowchart of an embodiment of a method ofconfiguration of a nuclear gauge according to the present subjectmatter;

FIG. 29 illustrates a schematic view of an embodiment of a nuclear gaugein communication with a nuclear gauge calibration system according tothe present subject matter;

FIG. 30 illustrates a flowchart of an embodiment of a method ofcalibration of a nuclear gauge according to the present subject matter;

FIG. 31 illustrates a flowchart of an embodiment of a method ofcalibration of a nuclear gauge according to the present subject matter;

FIG. 32 illustrates a flowchart of a partial embodiment of a method ofcalibration of a nuclear gauge according to the present subject matter;

FIG. 33 illustrates an embodiment of a density tracking chart that canbe use in an embodiment of a method of calibration of a nuclear gaugeaccording to the present subject matter; and

FIG. 34 illustrates an embodiment of a moisture tracking chart that canbe use in an embodiment of a method of calibration of a nuclear gaugeaccording to the present subject matter.

DETAILED DESCRIPTION

Reference will now be made in detail to the description of the presentsubject matter, one or more examples of which are shown in the figures.Each example is provided to explain the subject matter and not as alimitation. In fact, features illustrated or described as part of oneembodiment can be used in another embodiment to yield still a furtherembodiment. It is intended that the present subject matter cover suchmodifications and variations.

Nuclear Gauge Apparatus

FIGS. 1 and 2 illustrate a nuclear gauge, generally designated 10.Different aspects and elements of gauge 10 will be briefly describedwith a more detailed description of the different elements providedfurther below. The nuclear gauge can be a density gauge, a bulk densitygauge, a thin overlay gauge, a thin layer gauge, or a combinationthereof.

By way of example to explain the present subject matter, the gauge 10depicted in the figures is a thin layer gauge. However, as stated above,the gauge 10 can be other configurations of nuclear gauges. The gauge 10can be capable of accurately measuring the density of materials, forexample, thin layers of materials such as asphalt, through the use of ascattered radiation that is detected by radiation detectors. The gauge10 can operate in both backscatter and direct transmission modes. Thegauge 10 can include a gauge housing 12 and a tower, or source rodhousing, 30. The gauge housing 12 and the tower 30 can form a verticalconduit 32 that extends through both gauge housing 12 and tower 30. Forexample, the gauge housing 12 can have a vertical cavity 14 therein andthe tower 30 can include a vertical channel 34 therein that can bealigned to create the vertical conduit 32. For instance, the gaugehousing 12 can include a top cover 12A and a base 12B. The base 12B caninclude the vertical cavity 14 therethrough. The top can include anopening 15 through which the tower 30 can pass. The tower 30 can bedisposed on the base 12B of the gauge housing 12 so that the verticalchannel 32 aligns with the vertical cavity 14 to form a vertical conduit34 through the tower 30 and the gauge housing 12.

The gauge 10 can include a user interface 13 that is located on the topcover 12A of the gauge housing 12. The user interface 13 can be incommunication with a computing system, such as central processing unit(CPU) 17, that controls the gauge 10 and runs the associated tests. Forexample, the user interface 13 can include a screen 13A and keypad 13Bthat can be used to input the parameters of the tests to be run on thenuclear gauge 10.

The gauge 10 can include a vertically moveable source rod 20 containinga radiation source 22 in a distal end thereof. As shown in FIG. 14, thesource rod 20 can include a spacer 24, a ring weld 25, a source spring26 and a source plug 28. The radiation source 22 may be any suitableradiation source, such as ¹³⁷Cs radiation source or ⁶⁰Co. The source rod20 can reside in the vertical conduit 32 created by the vertical channel34 of the tower 30 and the vertical cavity 14 in the gauge housing 12.

The gauge 10 can include at least one density measurement system thatutilizes at least one radiation detector. For example, as shown in FIG.2, the gauge 10 can include two separate density measurement systems.The geometry of these two measurement systems is configured with respectto one another and with respect to the medium being measured in such amanner that they measure two different volumes of material. The twodifferent volumes are not mutually exclusive insofar as they partiallyoverlap one another. Measurement accuracy depends upon a larger portionof the volume measured by one of the measurement systems beingdistributed at a lower depth beneath the gauge than the volume measuredby the other measurement system. This is accomplished by placing oneradiation detection system in closer spatial proximity to the radiationsource than the other detection system. To accomplish this, the gauge 10includes a first radiation detector 18A and a second pair of radiationdetectors 18B, wherein the first radiation detector 18A is located incloser spatial proximity to the radiation source 22. The radiationdetectors, 18A and 18B, for example, may be any type of gamma rayradiation detector. For instance, the radiation detectors, 18A and 18B,can include preferably Geiger Mueller tubes, but can also includescintillation detectors, or proportional counters. The radiationdetectors, 18A and 18B, can be located adjacent to the base 12B of thegauge housing 12. The gauge 10 can also include a moisture detector 16that can use to measure the moisture of such construction material.

The gauge 10 can also include a handle 50 that is secured to the sourcerod 20 for vertically extending and retracting the source rod 20. Thehandle 50 along with a guide and sealing system 70 facilitate theguidance of the source rod 20 through the vertical conduit 32 created bythe vertical channel 34 in the tower 30 and the vertical cavity 14 inthe base 12B of the gauge housing 12. The handle 50 can be used to movethe source rod to a plurality of predetermined source rod locations soas to change the spatial relationship between the radiation source andthe at least one radiation detector. The handle 50 includes a coarseadjustment mechanism 52 and a fine adjustment element 54 for adjustingthe height of the source rod 20 for positioning the radiation source 22relative to the radiation detectors 18A, 18B to provide propermeasurement at the different predetermined source rod locations. Inparticular, the source location at backscatter is extremely importantand should be very precise.

To provide the predetermined source rod locations, an indexing mechanismcan be provided. For example, as shown in FIGS. 2-6, an indexpositioning strip 80 can be placed in the tower 30 that can be engagedby the handle 50 to hold the source rod 20 at a predetermined source rodlocation. The index positioning strip 80 can include index holes 82therein. The index holes 82 can serve as notches that the handle 50engages as will be explained in more detail below. The index holes 82can be uniformly spaced apart from each other. For example, the indexholes 82 can be spaced apart at interval distances of about one inch,about two inches or about three inches.

The tower 30 can include an indexing groove 36 that is adjacent andopens into the vertical channel 34. The index positioning strip 80 canbe secured in the indexing groove 36. The index positioning strip 80 canhave apertures 84 for accepting fasteners 84, such as screws, rivets orthe like that engage the tower 30. The index positioning strip 80 havingindex holes 82 therein can be securable at a designated location withinthe vertical channel 34 of the tower 30 to create the notches. Further,the index positioning strip 80 can be adjustable within the tower 30.

A depth strip 100, as shown in FIGS. 9-12, can be positioned in thetower 30 and can provide a non-contact measurement of the sourceposition. The depth strip can use optical sensors, such as optical rangefinder sensors, acoustic sensors, magnetic sensors and the like toprovide non-contact measuring of the positioning of the source rod. Forexample, the depth strip can include a plurality of Hall Effect depthsensors 102. Each of the depth sensors can be associated with at leastone of the source rod positions. The positioning of the source rod 20 atone of the source rod positions can activate one of the Hall Effectdepth sensors 102 for detecting the source rod position of the sourcerod 20. The depth strip 100 can comprise a source rod position detectioncircuitry 104 adapted for detecting activation of the depth sensors todetermine a current position of the source rod 20. This position can berelative from one another, or preferably absolute indicators.

The depth strip 100 can include a parting line 100A with the depth strip100 being convertible from a 12-inch unit to an 8-inch unit along theparting line 100A. Another parting line can be included on the depthstrip to create a depth strip that can be used in a backscatter onlygauge. To house the depth strip 100, the tower 30 can include ameasurement compartment 38. Depending on the type of depth strip 100,the measurement compartment 38 can be a separate channel or passagewayfor housing the depth strip.

Once the nuclear gauge 10 is assembled, the computing system, forexample, the CPU 17, can be configured to operate with a plurality ofoptions. Thereby, the nuclear gauge 10 can be configurable to operate ina plurality of settings. The computing system 17 can be configured toenable and to disable the settings of the nuclear gauge 10. A nucleargauge configuration system in communication with the computing system ofthe nuclear gauge 10 can also be provided. At the nuclear gaugeconfiguration system, commands can be communicated to the computingsystem 17 of the nuclear gauge 10 for one of enabling and disabling thesettings of the nuclear gauge 10.

To also ensure proper measurements using the gauge 10, a method forcalibrating a nuclear gauge is disclosed. The method includes providinga nuclear gauge 10 adapted to be remotely calibrated via encryptedcalibration communications. The nuclear gauge 10 can include a commandline interpreter function adapted for receiving calibration commands.Further, the method includes providing a nuclear gauge calibrationsystem in communication with the computing system 17 of the nucleargauge 10. The nuclear gauge calibration system is adapted to interrogatethe nuclear gauge for calibration information. The method includescommunicating, at the nuclear gauge calibration system, encryptedcommands to the nuclear gauge for calibrating the nuclear gauge.

The gauge 10 also includes a radiation shield assembly 90 as shown inFIGS. 2 and 17-24. The radiation shield assembly 90 includes a safetyshield 92 that is coaxially mounted in the base 12B of the gaugehousing. The safety shield 92 helps to define the vertical cavity 14 inthe base 12B of the gauge housing 12. For example, the base 12B isformed to create a shield housing 12D through which an opening passes.The safety shield 92 has a passage 92A passing therethrough. The safetyshield 92 fits into the shield housing 12D so that the opening in theshield housing 12D aligns with the passage 92A in the safety shield 92.A set screw 93 can secure the safety shield 92 in place by screwing theset screw 93 into a screw hole 93A in the shield housing 12D. Thealigned opening in the shield housing 12D and the passage 92A throughthe safety shield 92 can create the vertical cavity 14.

The radiation shield assembly 90 also includes a sliding block 94 thatis positionable to move laterally between two positions relative to thesafety shield 92. The sliding block 94 can reside in a first positionblocking a distal end of the vertical cavity 14 such that radiation isshielded from exiting the cavity. The sliding block 94 can also residein a second position adjacent to the vertical cavity. In the secondposition the source rod 20 can move vertically through the radiationshield assembly 90 and the base 12B of the gauge housing 12. The base12B of the gauge housing 12 and the safety shield 92 can define a track96 configured to receive the sliding block 94 and guide movement of thesliding block 94. For example, a shield track segment 92B can be definedin the safety shield 92 that comprises at least a portion of the track96. The shield track segment 92B and the passage 92A can intersect andmerge at the lower end of the safety shield 92 as shown in FIG. 21.

The base 12B of the gauge housing 12 can include a base track segment12C. The base track segment 12C and the shield track segment 92B can bealigned to form the track 96. The sliding block 94 can be placed in thetrack 96 formed by the base track segment 12C and the shield tracksegment 92B. In the first position of the sliding block 94, the slidingblock 94 extends through the shield track segment 92B such that an end94A of the sliding block abuts against an interior wall 92C of thesafety shield 92 as shown in FIG. 22. The portion of the interior wall92C that the sliding block 94 abuts can comprise a hardened material,such as hardened steel, as will be explained in more detail below. Inthis first position the vertical cavity 14 and the vertical conduit 32which it partially forms are closed by the sliding block 94. In thesecond position of the sliding block 94, the end 94A of the slidingblock 94 is moved away from the interior wall 92C of the safety shield92 so that the vertical cavity 14 and the vertical conduit 32 which itpartially forms are opened so that the source rod 20 can emerge. In sucha position, the sliding block 94 is adjacent the vertical cavity 14.

A spring 98 can engage the sliding block 94 to bias the sliding block 94into the first position. The spring 98 can engage the end 94B of thesliding block 94. Further, base 12 can include a spring guide 98A. Thespring 98 can reside between the spring guide 98A and the end 94B of thesliding block 94.

As shown in FIG. 2, the safety shield 90 and sliding block 94 of theradiation shield assembly 90 are operatively positioned to minimize theuser's exposure to radiation when the radiation source 22 is in the safeposition. The safety shield 90 can be constructed of lead or tungsten.However, other radiation shielding material may be used. The slidingblock 94 can also comprise radiation shielding material such astungsten.

The gauge 10 can include a remote user interface that can be used toinitiate a measurement of the gauge 10 in addition to the user interface13 on the gauge housing 12. For example, the remote user interface canbe a remote keypad 120 as shown in FIGS. 1-3 and 25B. The remote keypad120 can be located on a top of the tower 30 and distal from the gaugehousing 12. The remote keypad 120 can comprise multiple switch states.The states can include a start switch 122 and an escape switch 124. Thestart switch 122 can be used to begin a gauge count or other tests oncethe gauge 10 and source rod 20 are in a proper position. The escapeswitch 124 can be used to abort such tests. The tower 30 can include arouting compartment 39 for routing the electrical wiring for the secondkeypad 120 into the gauge housing 12 for connection with the CPU 17. Therouting compartment 39 can be a separate channel or a passageway withinthe tower 30. Alternatively, the remote keypad can be a wireless controlmechanism, such as a fob, which is physically separated from the gauge10 and is in wireless communication with the gauge 10.

The gauge 10 can include counting circuitry that is used to countpulses. For example, the gauge 10 can have a pulse counting circuitpackage 160 as shown in FIG. 26. The circuit package 160 can includemultiple identical counting circuits such as 162 and 164. The circuit162 is for the density measurement and the circuit 164 for the moisturemeasurement. Each circuit 162, 164 can include a 4-bit binary ripplecounter 166, 168 so that the circuit package 160 has dual 4-bit binaryripple counters 166, 168. The counters 166, 168 can be designed to countto eight bits (255) by connecting the output of one 4-bit counter to theclock input of the other counter in the package 160. In one embodiment,every negative transition on the input A will cause the counter toincrement by one. Exemplary sensors for the density circuit can be GM,proportional, avalanche, solid state, and scintillation detectors.Sensors for the moisture circuit can be He³ proportional, or evenelectromagnetic in nature.

The counters 166, 168 are reset and enabled by two control lines fromthe CPU 17: an enabling control line 170 (CNT_EN) and a reset controlline 172 (CNT_RESET). When control line 170 carries a high signal(CNT_EN), the counters 166, 168 are disabled. This sets an output froman OR gate 178 on line 174 to high and an output of an OR gate 180 online 176 to high and disables the G-M and He³ pulses. The counters 166,168 are then reset to zero when the signal (CNT_RESET) from resetcontrol line 172 is high. The signals (CNT_EN) and (CNT_RESET) are logic1 to reset the counter 166, 168 to zero and disable counting. When thesignal (CNT_RESET) from reset control line 172 and the signal (CNT_EN)from control line 170 CNT_ENABLE are low, the counters 166, 168 willcount pulses from, for example, the G-M and He³ tubes.

Since the counters' maximum count is 255, the microcontroller on the CPU17 regularly reads the counter outputs QA, QB, QC, QD, QA1, QB1, QC1,and QD1 from lines 182 and lines 184 to look for overflow. When thecounter output QA, QB, QC, QD, QA1, QB1, QC1, QD1 changes from low tohigh and back to low, the software increments its internal counter by256. For example, the counter output QA can transition from low to highand back to low every two counts, the counter output QB can transitionfrom low to high and back to low every four counts, and so on. When thecount time is finished, the CPU 17 reads the lower order bits from eachcounter. Also, when the count time stops, the CPU 17 will set signal(CNT_EN) high.

The CPU 17 can only read one output from the counters 166, 168 at atime. Circuit 162 includes an 8-to-1 multiplexer 186 and circuit 164includes an 8-to-1 multiplexer 188. Each 8-to-1 multiplexer 186, 188 isused to select which counter output the CPU 17 will read. Three controllines from the CPU 17 (SELA, SELB, and SELC) make the selection. Thecontrol lines (SELA, SELB, and SELC) are high as the CPU 17 monitors theoutput QD1 for overflow. During the counting time, the counter outputcan be monitored and SELA, SELB, and SELC all equal to 1. At the end ofa count, the signal (CNT_EN) from control line 170 goes low to disablecounting, and then the selection lines increment from binary 000 tobinary 111, while the CPU 17 reads each output line.

A primary function of the gauge 10 is to collect and store informationin user created projects. This project information is kept in electronicmemory in the CPU 17 in the gauge 10. This information can betransferred to a computer, such as a personal computer using a serialcable connection between the personal computer's com port and thegauge's com port. Then, the data is transmitted from the gauge 10 to thepersonal computer. This process means that the user must bring the gauge10 close to the personal computer (within the serial cable length),start a data transfer program (mainly using a terminal emulationprogram), and instruct the gauge 10 to transfer the data.

Alternatively, a portable storage device can be used to transfer thedata. Some embodiments of gauge 10 can use USB based mass storagedevices to transfer this information. A USB hosting device that supportsa USB mass storage device interface can be used inside the gauge 10. Thehosting device has a USB port as shown in FIG. 1 and a serial port (notshown). The gauge 10 can communicate with the hosting device over theserial port, and the hosting device controls a USB mass storage deviceplaced in the USB port. Project information can be sent to the USB massstorage device while it is in the USB port 19 on the gauge 10. Then theUSB mass storage device can be removed. It can then be taken to acomputer such as a personal computer and plugged into the personalcomputer's USB port. The user can then move the project information fromthe USB mass storage device to the PC's internal memory for further useslike creating reports, printing the project, or importing the data intoa spread-sheet.

The gauge 10 can include a global positioning system (GPS) receiver 17Bas shown in FIG. 2 that is in communication with the CPU 17. The GPSreceiver 17B can be used to update the clock/calendar in a gauge 10. AGPS receiver 17B can receive time information from satellites. Thisinformation can be set relative to the time at 0 degrees longitude(GMT). If the gauge users set the hour offset for their local time zonewith respect to GMT time, the gauge can keep its clock/calendarcorrected whenever a GPS signal is received. The gauge simply adds theoffset to the GPS supplied time, checks the gauge's clock/calendar, andcorrects the reading if needed. An additional method to achieveautomatic time/date updates can be to have antennae circuitry that isconfigured to receive 60 kHz VLF radio time signals transmitted by NISTfrom station WWVB near the US atomic clock in Boulder, Colo. This sametechnology is used to update so called “atomic clocks”.

The gauge 10 can have the capability to ask the users what time zoneoffset they would like (up to +/−12 hours), and store that offset innon-volatile memory. With the integration of a GPS receiver 17B in amoisture density gauge 10, the time and/or date can be automaticallyupdated from the data acquired from the GPS receiver 17B. Depending onthe NEMA mode of the GPS receiver 17B, every reading can contain atime/date stamp accurate to within nanoseconds.

The use of the GPS receiver 17B can also be used to improve the qualityof readings taken by the gauge 10. A practice of some moisture densitygauge operators is to find a “good” or acceptable measurement locationand to take consecutive readings claiming these readings were acquiredat multiple locations on an asphalt mat. Because the time function on amoisture density gauge is currently adjustable by the operator, theactual reading time record can be altered before making a measurement.If the time/date adjustment is unavailable to the gauge operator and isinstead automatically managed by collecting the information from the GPSreceiver 17B, every reading stored in memory could have an accuratetime/date stamp. In addition, the time/date information can beassociated with the location information thus making it impossible to“fudge” or manipulate the data collected. In this manner, the quality ofthe readings taken by the gauge 10 can be improved by reducing theopportunity for erroneous measurement locations to be reported.

An embodiment of the tower 30, handle 50, radiation shield assembly 90and other related features will now be described in more detail. Thetower, or source rod housing, 30 as shown in FIGS. 1-8 providessturdiness and durability to protect the source rod 20. The tower 30 cansubstantially surround the source rod 20. The tower 30 provides astructure that supports the source rod 20 and limits the amount ofstress placed on the source rod 20 that can occur by an unintendedclockwise or counterclockwise torque. Such torque can occur when thesource rod 20 is in a safe position. Thereby, the tower 30 provides astiffer source rod 20 positioning as compared to gauges without a tower.The tower 30 can have any cross-sectional shape. For example, the tower30 may have a cross-section that is circular, square, rectangular or thelike. Further, as shown in the drawings, the tower 30 can have atriangular cross-section. The tower 30 can comprise a metal or ahardened plastic. For example, the tower 30 can be extruded aluminum.

The channel 34 in tower 30 is wide enough to provide sufficientclearance for the source rod. For example, as shown in FIG. 4B, thechannel 34 can have a circular cross-sectional diameter D₁ that provideseasy movement of the source rod 20 therein. The channel 34 can have aninlet 34A that is formed by edges 30B and opens to a side 30A of thetower 30. The handle 50 affixed to the source rod 20 can be configuredto slidably engage the inlet 34A. Handle 50 can have a grip portion 50Athat extends outward from the tower 30, an engagement portion 50B thatis adjustably connected the source rod 20 and a neck portion 50C that isdisposed between the grip portion 50A and the engagement portion 50B.The inlet 34A can have a width W₁ in which the neck portion 50C canreside. The width W₁ of inlet 34A can be less than the diameter or widthof the source rod 20.

The engagement portion 50B can be configured to slidably engage thechannel 34. For example, the handle 50 can include slider pads 51Cand/or at least one slider disc as shown in FIG. 13C. In the embodimentshown in FIGS. 13A-13D, a top slider disc 51A and a bottom slider disc51B are provided that are positioned on either end of the engagementportion 50B of the handle 50. The slider discs 51A, 51B can have across-sectional shape taken in a plane parallel to the grip portion 50Aof the slider discs 51A, 51B that is larger than the cross-sectionalshape of the engagement portion 50B. For example, the cross-sectionalview of the engagement portion 50B below the grip portion 50A and theneck portion 50C illustrated in FIG. 13D shows the outer diameter S₂ ofthe of the bottom slider disc 51A being larger than the outer diameterS₁ of the engagement portion 50B. The cross-sectional shapes of the topand bottom slider discs 51A, 51B can be approximately the same size. Forexample, the outer diameters of the top and bottom slider discs 51A, 51Bcan be equal. The outer diameters of the top and bottom slider discs51A, 51B can be similar in size to the diameter D₁ of the verticalchannel 34 of the tower 30. Thereby, the slider discs 51A, 51B canenhance the stability of the source rod 20 in the vertical channel 34 ofthe tower 30 and can assist in reducing radial movement of the sourcerod 20 at the end engaged by the handle 50.

The slider discs 51A, 51B can be at least partially formed from afriction reducing material. For instance, the slider discs 51A, 51B canhave an outer perimeter that interfaces with the tower 30 in thevertical channel 34 that is a friction reducing material. For example,the slider discs 51A, 51B can be or can include a polymer having a lowcoefficient of friction. The polymer can be at least one ofpolytetrafluoroethylene, perfluoroalkoxy, and fluorinated ethylenepropylene.

The handle 50 can include a plunger 56 and a trigger 58. The plunger 56can be extendable to engage index holes 82 of the index positioningstrip 80 disposed within the tower 30 and retractable to disengage theindex holes 82 by actuation of the trigger 58. The trigger 58 can belocated on the underside of the grip portion 50A of the handle 50. Thetrigger 58 can be held in place by a pair of pins 58A, 58B. The end ofthe trigger 58 distal from the neck portion 50C of the handle 50 canhave a pivot groove 58C that engages pivot pin 58A to create a pivotpoint for the trigger 58. The pivot pin 58A can reside in the pivotaperture 53A defined in the grip portion 50A. The trigger 58 can includea vertical extending slot 58D as shown in FIGS. 2 and 13C that canengage locking pin 58B. The slot 58D permits the trigger 58 to be movedup and down with the pin 58B residing in the slot 58D. A trigger spring59 can engage the trigger 58 at a position on the trigger closer to theslot 58D and more distal from the groove 58C. The trigger spring 59biases the trigger 58 away from the plunger 56. The handle 50 can alsoinclude a spring 60 that engages the plunger 56 and a spring guide 62within the grip portion 50A. The spring 60 biases the plunger 56 towardsan extended position.

The trigger 58 can include at least one protrusion 58E that engages atleast one retraction groove 56A on the plunger 56. In the embodimentshown, two protrusions 58E are provided on the trigger 58 and tworetraction grooves 56A are provided on the plunger 56. However, it isunderstood that one or more protrusions and corresponding retractiongrooves may be provided.

The protrusions 58E can be slanted to match a slant in the groove 56A.The slant of the protrusions 58E and the retraction grooves 56A are suchthat, as the trigger 58 is squeezed upward, the protrusions 58E engagethe retraction grooves 56A forcing the plunger 56 to a retractedposition. Once the source rod is moved to one of the predeterminedsource rod locations that is aligned with a corresponding index hole 82,the trigger 58 can be released. The trigger spring 59 biases the trigger58 away from the plunger 56 and the spring 60 biases the plunger 56towards an extended position with the plunger 56 engaging thecorresponding index hole 82.

The index holes 82 of the index positioning strip 80 can providedifferent source rod locations by holding the source rod 20 at differentpositions as shown in FIGS. 2-6. These locations can include, forexample, index hole 82A as shown in FIG. 6 that corresponds to the“safe” position wherein the radiation source 22 is raised and shieldedfrom the test material. The safe position is used to determine thestandard count. Another index hole 82B corresponds to the backscattermode wherein the radiation source 22 is located adjacent to the surfaceof the test material underlying the gauge 10. Other index holes 82 cancorrespond to a plurality of direct transmission positions. The use ofthe index positioning strip 80 with its adjustability permits lessstringent manufacturing tolerances. Therefore, the index positioningstrips 80 allow greater variability with this design. Thus, the positionof the strip 80 can be adjusted for additional manufacturingflexibility. The strip 80 can be attached in different manners. Forexample, the tower 30 can include adjustment screw holes 36A (see FIG.2) that can align with apertures 84 in strip 80 for insertion of screws.Thus, adjustment screw holes 36A and apertures 84 can be used to securethe strip 80 to the tower 30. The index positioning strip 80 can beconvertible to a length that can be used with a 12-inch source rod, an8-inch, or to a length that is usable with a backscatter only gauge.

The safe position corresponding to the index holes 82A can position thetip of the source rod 20 at least about 2.20 inches above the outersurface of the base 12B of the gauge housing 12. This places theradiation source 22 in a position that exhibits reduced sensitivity ofthe standard count to slight radiation source positioning variability inthe vertical direction. Specifically, the radiation standard count ratewith the radiation source 22 in the safe position changes only about2-10 scaled counts per mil of radiation source position change in thevertical direction in the gauge 10.

As illustrated in FIGS. 9-11, a depth strip 100 can be positioned in thetower 50 and can provide non-contact measurements used to determine thedepth at which the source rod 20 is positioned during use. For example,the tower 50 can include a measurement compartment 38 in which the depthstrip 100 can be placed. The measurement compartment 38 can be a channelor groove. Alternatively, the compartment 38 can be a passageway withinthe tower 30 in proximity to the vertical channel 34 in which the sourcerod 20 resides. As stated above, the depth strip can use opticalsensors, such as optical range finder sensors, acoustic sensors,magnetic sensors and the like to provide non-contact measuring of thepositioning of the source rod.

As described above, the depth strip 100 that resides in the measurementcompartment 38 can be a sensor that uses magnetically actuated, lowpower Hall Effect sensors 102 as the means to determine the rodposition. For example, the Hall Effect sensors 102 of the depth strip100 can be alignable with the index holes 82 of the index positioningstrip 80. The Hall Effect sensors 102 can be mounted on a source rodposition detection circuitry, such as a printed circuit board, 104 atdiscrete positions which are spaced about one inch and/or about twoinches apart. The printed circuit board 104 can include otherelectronics to power the Hall Effect sensors 102, determine which HallEffect sensor 102 is activated, and communicate this information withthe gauge CPU 17 that is in communication with the user interface 13.This configuration allows for absolute location of the source rod, notjust relative to the safe position.

The handle 50 can include a magnet 64 thereon that is detectable by theHall Effect sensors 102 to provide non-contact measuring of thepositioning of the source rod 20. The Hall Effect sensors 102 can beplaced on the printed circuit board 104 so that they will line up withthe magnet 64 located on the handle 50 of the moveable source rod 20.The source rod 20 can be then “indexed”, such that it can only be placedin discrete positions through the use of the index positioning strip 80.These positions can be about one inch or about two inches apart. Specialindexing is also achievable by replacing the strip. At each of thesediscrete positions, the magnet 64 in the handle 50 can be positioneddirectly across from one of the Hall Effect sensors 102 on the printedcircuit board 104. Thus, only one of the Hall Effect sensors 102 isactuated at a time. When the user starts a gauge operation that issource rod position sensitive, the CPU 17 can communicate with theprinted circuit board 104 electronics to determine which Hall Effectsensor 102 is activated. The CPU 17 software can be structured such thatit can relate the actuated Hall Effect sensor 102 to a known indexposition. If a Hall Effect sensor 102 is not actuated, the CPU 17 caninform the gauge user that the source rod 20 is not in a valid position.If a Hall Effect sensor 102 is actuated, the CPU 17 can start the gaugeoperation, and pass the index position to the software. In this manner,the gauge user does not have to manually enter the source rod position.

By including a parting line 100A along the printed circuit board 104,the depth strip 100 is convertible from a 12-inch unit to an 8-inch unitalong the parting line. In this manner, a single designed depth strip100 can be used in different gauges 10 that have two different distancesat which the source rod 20 can extend. For 8-inch units, the depth strip100 can be parted at this parting line 100A. When not parted, the wholedepth strip 100 can be used for 12-inch units. The depth strip 100 caninclude wiring 106 that can be use to connect it to the CPU 17 and/orpower source of the gauge 10.

Before the attachment of the tower 30 to the base 12B of the gaugehousing 12, the depth strip 100 can be inserted into the measurementcompartment 38 of the tower 30 so that the depth strip is in the properlocation to determine the source rod locations based on the position ofthe indexing holes 82 of the index positioning strip 80. If thecompartment 39 is a passageway, the depth strip 100 can be inserted intothe measurement compartment at the bottom of the tower 30 so that thetop of depth strip 100 extends through the top of the tower 30. Aplacement pin 100B can be inserted into an aperture 100C in the depthstrip 100. After the insertion of the pin 100B, the depth strip 100 canbe pushed back into the tower 30 so that the pin 100B engages the top ofthe tower 30 so that the Hall Effect sensors 102 align with the indexholes 82 of the index positioning strip 80. For example, the tower caninclude a seat that receives the pin 100B. After insertion, theintegrated circuits, or Hall Effect sensors, 102 of the printed circuitboard 104 of the depth strip 100 should face the vertical channel 34where the source rod 100 will reside after insertion into the tower 30.The tower 30 can include a wiring aperture 108 through which the wiring106 can be pulled as shown in FIG. 12. The wiring 106 can then beproperly connected to the gauge 10.

To facilitate proper movement of the source rod 20 within the verticalconduit 32 formed by the vertical channel 34 in the tower 30 and thevertical cavity 14 in the gauge housing 12, the guide and sealing system70 can be provided. The guide and sealing system 70, as shown in FIGS.1, 2 and 4-8, can work in conjunction with the at least one slider discon the handle 50, such as slider discs 51A, 51B, to increase stabilityand minimize radial movement of the source rod 20. The guide and sealingsystem 70 can include a bracket 72 that can be placed and secured in thevertical channel 34 of the tower.

The bracket 72 can have a first end portion 72A that is configured tolie flat within the groove 36 in the tower 30. The first end 72A portioncan be secured below the index positioning strip 80, but aligned withthe index positioning strip 80 within the groove 36. The bracket 72 canalso have a second end portion 72B that is configured to reside outsideof the channel 34 of the tower 30. For example, as shown in FIGS. 4-6,the second end portion 72B can be wider than the width W₁ of the inlet34. The tower 30 can have a groove 30C cut into each of the edges 30B oneither side of the inlet 34A of the channel 34. The second end portion72B can be configured to reside in the grooves 30C. The second endportion 72B can extend substantially parallel to the first end portion72A of the bracket 72. Between the first end portion 72A and the secondend portion 72B, the bracket 72 can include a mid-portion 72C. Themid-portion 72C can be substantially perpendicular to both the first endportion 72A and the second end portion 72B and also about perpendicularto the vertical channel 34 in which the source rod is disposable. Themid-portion 72C includes a bracket aperture 72D through which the sourcerod can pass. The edges 30B can also include slots 30D through which thebracket 72 including the mid-portion 72 can pass so that when thebracket 72 is secured in the tower 30, the first end portion 72A resideswithin the groove 36, the second end portion 72B resides within thegrooves 30C, and the mid-portion 72B extends through the slots 30D andinto the vertical channel 34 so that the bracket aperture 72D alignswith the vertical channel 34 to accept the passage of the source rod 20therethrough.

The guide and sealing system 70 (see FIG. 2) can also include an upperseal 74 that can be placed into the vertical channel 34 below thebracket 72 so that the upper seal abuts against the underside of themid-portion 72C of the bracket. The upper seal 74 can have an innerdiameter that is less than the diameter of the bracket aperture 72D andis in close tolerance of the source rod 20. The outer diameter of theupper seal 74 can be substantially similar to the diameter D₁ of thevertical channel 34. After the upper seal 74 is seated against thebracket 72, a tube spacer 76 with a grease fitting 76A can be seatedagainst the upper seal 74. The guide and sealing system 70 can alsoinclude a source bearing 78 that can be secured against the tube spacer76 at the end distal from the bracket 72 and upper seal 74. The sourcerod bearing 78 can include a seal wiper 78A that acts as a lower seal.The source rod bearing 78 can be seated in the shield housing 12D of thebase 12B above the radiation shield assembly 90. The tube spacer 76 caninclude a top washer 76B and a bottom washer 76C that can be placed oneither end of the tube spacer. For example, top washer 76B can be placedon the end of the tube spacer 76 proximate to the upper seal 74 and thebottom washer 76C can be placed at the end of the tube spacer 76proximate to the source rod bearing 78. The source rod bearing 78 can bea bushing. The source rod bearing 78 can guide the source rod 20 throughcavity 14 in the gauge housing 12 with an extremely close fit to thesource rod 20 in order to minimize variability in radiation sourcepositioning. Specifically, the outer diameter of source rod bearing 78can be about 1.1265 inches+/−about 0.0005 of an inch and the bearinginner diameter can be about 0.6265 of an inch+/−about 0.0005 of an inch.Additionally, the bearing housing diameter can be about 1.1265inches+/−0.0005 of an inch. The source rod 20 diameter can be about0.625 of an inch+/−about 0.001 of an inch. This results in a nominalbearing clearance of about 0.00025 of an inch and a bearing clearancerange of press-fit to about 0.001 of an inch. The nominal source rodclearance can be about 0.00175 of an inch and the source rod clearancerange can be from about 0.0005 to about 0.0030 of an inch. Thus, thesource rod 20 has a total range of radial movement of no more than about0.0005 of an inch to about 0.0040 of an inch. Since the desired positionof the source rod 20 is on the true centerline of the source rod bearing78, the movement away from true center is actually the radial clearance,which equals one-half of the diametrical clearance. Thus, the maximummovement away from true center of the source rod 20 can be aboutone-half of 0.0040 of an inch, or 0.0020 of an inch.

It is important to correctly calibrate the height of the source rod 20to ensure that the source rod 20 will be at the correct depths when thehandle engages the index positioning strip 80. To calibrate the gauge10, the exact source height can be adjusted in real time by the assemblytechnician using only a wrench or a screwdriver. The screwdriver orwrench can be inserted into a threaded device, such as a screw or bolt54A that is securely affixed to the source rod 20 such that as the screwdoes not rotate separate from the source rod. Any type of finely pitchedthread device can be used. A screw such as a flathead screw, slottedscrew, a Phillips head screw, a star screw such as those sold under thename TORX®, a spline drive screw, hex screw, double hex screw or thelike, can be used as the fine adjustment element 54. Similarly, an AllenHead screw can be used.

Access is can be permitted to the screwdriver or wrench through the topof the tower 30 and the handle 50. The remote keypad 120 or other topportion is removed. The handle 50 can define at least one adjustmentaperture therein to permit access to the fine adjustment element 54. Forexample, the handle 50 includes adjustment apertures 66 and 68 as shownin FIGS. 2, 13B, and 14 in both the engagement portion 50B and theplunger 56, respectively, so that when the source rod 20 is inbackscatter position all the adjustment apertures 66 and 68 in thehandle 50 are aligned within reach of the assembly technician'sscrewdriver or wrench. In the embodiments where the handle 50 caninclude a plunger 56 and a trigger 58, the plunger 56 can define anadjustment aperture 68 that aligns with the adjustment aperture 66 inthe handle 50 when the plunger 56 resides in an extended position.

The coarse adjustment mechanism 52 and fine adjustment element 54, asshown in FIGS. 2 and 14, can be used to set the height of the source rod20 during manufacturing with the settings being permanent orsemi-permanent. “Semi-permanent” as used herein means that the height ofthe source rod 20 cannot be reset without physical manipulation throughthe use of chemical and/or mechanical tools. The handle 50 can alsoinclude one or more set screws 69 for holding and locking the source rod20 in place after the height of the source rod 20 is adjusted with thecoarse adjustment mechanism 52 and the fine adjustment element 54. Thesource rod 20 can be in a backscatter position when the height of thesource rod 20 is adjusted with the coarse adjustment mechanism 52 andthe fine adjustment element 54. This ability greatly reduces assemblytime, improves locating precision and repeatability.

Within the handle 50, the coarse adjustment mechanism 52 can include athreaded section 52A and the fine adjustment element 54 can include ascrew, such as an Allen Head screw 54A. Such an Allen Head screw 54A canbe securely affixed to the source rod 20 such that the screw does notrotate separately from the source rod 20.

The coarse adjustment mechanism 52 permits the quick attachment of thesource rod 20 into the handle 50. The fine adjustment element 54 usesthe threaded section 52A as well, but fine adjustment element 54 permitsfor very small incremental movement of the source rod 20 through partialrotation of the source rod 20. The fine adjustment element 54 can permitaccurate and acute adjustment of the height of the source rod of lessthan about one hundredth of an inch. For example, the fine adjustmentelement 54 can permit adjustment of the source rod 20 to plus or minusabout 0.005 of an inch. In some embodiments, the fine adjustment element54 can permit adjustment of the source rod 20 to plus or minus about0.001 of an inch. Thus, both coarse adjustments and fine adjustments canbe made to the source rod height.

In the past, attempts have been made to keep water out of the gauges.Humidity and water can adversely affect the high voltage electronics.The problem has always been to develop a seal that allows the source tomove freely up and down while completely blocking humidity and moisture.To protect the electronics contained within the gauge housing 12 of thegauge 10, precautions can be taken to ensure a good seal is createdbetween the top cover 12A and the base 12B of the gauge housing 12 andbetween the tower 30 and the gauge housing 12. For example, as shown inFIG. 16, an O-ring 130 can be positionable in a groove 132 within thebase 12B of the gauge housing 12 between the base 12B and the top cover12A. The O-ring 130 can extend around an outer parameter of the base 12Bwith the top cover 12A engaging the O-ring 130 to create water proofseal between the top cover 12A and the base 12B.

Further, as shown in FIGS. 2 and 25A-25C, a second O-ring 134 having adiameter which fits tightly around the cross-section of the tower 30 canbe positioned at the tower base where the tower 30 is secured to thegauge housing 12. The use of the O-ring 134 and a trim plate 138 thatfit around the horizontal cross-sectional shape of the tower 30 andengage the top cover 12A of the gauge housing 12 allows the entirecircumference of the sealing area to be water tight. This can beespecially important in gauges that are specified for all weather use.For example, the cross-section of the tower 30 can be triangular inshape and the top cover 12A can form a groove 136 around opening 15 intowhich tower 30 can extend. A triangular trim plate 138 having an outeredge 139 can push the second O-ring 134 against the tower 30 to create awater resistant seal. The trim plate 138 can be placed around the towerbase and over this second O-ring 134 and then secured to the gaugehousing 12.

The radiation shield assembly 90 is described below in more detail. Asstated above, the radiation shield assembly 90 has a portion that isoperatively positionable to move laterally between two positions. Afirst position is provided for blocking a distal end 14A of the verticalcavity 14 of the gauge housing 12 such that radiation is shielded fromexiting the cavity 14. A second position adjacent to the vertical cavity14 is provided for allowing vertical movement of the source rod 20through the radiation shield assembly 90. As described above, theradiation shield assembly 90 can include a sliding block 94 positionableto move laterally between the first position and the second position. Atrack 96 can be configured to receive the sliding block 94 and guidemovement of the sliding block 94. A spring 98 can engage the slidingblock 94 and bias the sliding block 94 into the first position.

A safety shield 92 can be included in the radiation shield assembly 90.The safety shield 92 can include a shield track segment 92B therein thatcomprises at least a portion of the track 96. The base 12B of the gaugehousing 12 can include a base track segment 12C. The base track segment12C and the shield track segment 92B are alignable to form the track 96.

At least one replaceable sliding guide 140, as shown in FIGS. 17 and18A-18C, is positionable within the track 96 adjacent the sliding block94. The at least one replaceable sliding guide 140 is configured toreduce friction as the sliding block 94 moves between the first positionand the second position. The at least one replaceable sliding guide 140can comprise two replaceable sliding guides 140 with each replaceablesliding guide 140 extending over at least a portion of the base tracksegment 12C and the shield track segment 92B on opposing walls of thetrack 96. The track 96 is configured to extend in a direction within thenuclear gauge 10 so that, as the sliding block 94 moves from the firstposition to the second position, the sliding block 94 moves away fromthe radiation detector(s) 18A, 18B as shown in FIG. 16 with the slidingblock housing 12D′. The track 96 can extend at an angle α of betweenabout 90° and about 180° as measured from a plane M extending betweenthe radiation detector(s) 18A, 18B and the point of the track 96 closestto the radiation detector 18A as shown in FIG. 17. In some embodiments,the track 96 can extend at an angle α of between about 100° and about135°. The angle α of the track can bias the sliding block 94 toward aclosed position due to gravity when the gauge is placed in a carryingcase and the carrying case is in its upright position. Further, at suchan angle, the effect of the sliding block 94 on the reading of the gauge10 is minimized as any leakage of radiation is directed away from thedetectors.

As stated above, the safety shield can be a molded block. The safetyshield 92 can be made of lead. Alternatively, the safety shield 92 canbe tungsten or a tungsten and lead mix. For example, the safety shield92 can comprise concentric cylinders of lead and tungsten. The shieldtrack segment 92B can include two opposing side walls 92D extending intothe safety shield 92 and an end wall 92C disposed between the side walls92D (see FIG. 21) within the safety shield 92 with at least a portion ofthe end wall 92C within the safety shield 92 comprising a hard surfacematerial. The safety shield 92 can include wear plates, or inserts, of ahard surface material that forms the end wall 92C. The hard surfacematerial can comprise at least one of steel, hardened steel, high carbonsteel, stainless steel, tungsten or the like.

The at least one replaceable sliding guide 140 shown in FIGS. 18A-18Ccan be or can include a polymer having a low coefficient of friction.The polymer can be at least one of polytetrafluoroethylene,perfluoroalkoxy, and fluorinated ethylene propylene. The at least onereplaceable sliding guide 140 can include a body 142 and an arm 144extending outward from the body 142. The body 142 can include arectangular shape with a base side 146 and the arm 144 can comprise adifferent rectangular shape extending from the base side 146, whereinthe body 142 has a height that is larger than a height of the arm 144thereby forming a notch 148 in the at least one replaceable slidingguide 140.

In such embodiments, the safety shield 92 can define an indentation 99,as shown in FIG. 17, configured to receive the arm 144 of the at leastone replaceable sliding guide 140 so that an outer surface 140A of theat least one replaceable sliding guide 140 is about flush with an outersurface of shield track segment 92B of the safety shield 92. The arm 144by engaging the indentation 99 can minimize rotation of the slidingguide 140 in the safety shield 92 caused by movement of the slidingblock 94. In embodiments where the base 12B of the gauge housing 12includes a base track segment 12C and the base track segment 12C and theshield track segment 92B are alignable to form the track 96, the basetrack segment 12C can have a width that is larger than the width of theshield track segment 92B for receiving the body 142 of the at least onereplaceable sliding guide 140.

A cover plate 150 for securing the radiation shield assembly 90 withinthe gauge housing 12 can be included with the radiation shield assembly90. The cover 150 can be a scraper plate that includes a scraper 152.The scraper ring 152 can be held in place in the cover plate 150 by aring retainer 154 as shown in FIG. 24. The cover plate 150 can be placedin a recess 97 in the lower surface 12E of the base 12B of the gaugehousing 12. Once installed, the cover plate 150 can abut the base side144A of the at least one replaceable sliding guide 140. The outersurface of the cover plate 150 can be flush with the lower surface 12Eof the base 12B. The cover plate 150 is positioned on the base 12B at anangle that covers the rest of the radiation shield assembly 90 and suchthat the entire radiation shield assembly 90 is contained inside thebase 12B underneath the cover plate 150.

Referring back to the remote keypad 120 as shown in FIGS. 1-3 and 25B,such a keypad 120 located at the end of the tower 30 distal from thegauge housing 12 is intended to reduce the amount of bending and/orstooping required by the operator of the gauge 10. The operator'sgreatest benefit is gained while using the gauge 10 on an asphalt mat inthe backscatter position. The operator will identify a measurementlocation on the asphalt mat. The operator will then move the source rod20 to the backscatter position of approximately contacting the surface(the transmission mode assumes a BS position of zero, true that it isabout 2 inches from safe position, but safe is not zero). The operatorcan then, with very little movement, press the start switch 122 toinitiate the gauge counting. The location of the remote keypad 120 whenlocated on the end of the tower 30 distal from the gauge housing 12 canbe approximately two feet off of the asphalt mat and remains at thatdistance regardless of the source rod position.

Alternatively, the operator can identify the measurement location, placethe source rod 20 in the backscatter position and then press a startswitch on the user interface 13 of the gauge 12 located on the gaugehousing 12. The location of the user interface 13 on the gauge housing12 is approximately 5 to 6 inches off of the asphalt mat. Typically, topress the start switch on the user interface 13 located on the gaugehousing 12 to initiate a gauge count, the operator will have to bendtheir back all of the way forward or stoop down closer to the asphaltmat to begin a gauge count. While the use of the remote keypad 120provides a more ergonomically safe method to operate the gauge 10,either the remote keypad 120 or the user interface 13 on the gaugehousing 12 can be used.

Thus, the first and second user interfaces 13 and 120 share somefunctionality with the first and second user interfaces with eachincluding at least one keypad switch having functionality forcommunicating the same user input to the nuclear gauge computing system.For example, both the remote keypad 120 and the user interface 13 on thegauge housing can share the “start” and “escape” functions in theembodiment shown, since the remote keypad 120 includes both a startswitch 122 and an escape switch 124. Electrically, the start switch 122and escape switch 124 can be wired in parallel to the same two keys onthe user interface 13 located on the gauge housing 12. The firmwareoperating the gauge 10 can be written in a manner that will allow asingle key press of the start switch 122 to begin a gauge count andallow the operator to store that gauge count information in a gaugememory in the CPU 17 with an additional single key press of the startswitch 122. Alternatively, an I/O interrupt could be initialed by startswitch 122 letting the gauge software enter the requested state, such asstarting a count or measurement.

The remote keypad 120 can be located on the stationary support tower 30.This tower 30 provides an excellent location for a stationary keypad anda routing compartment 39 to route electrical wiring 126 from the remotekeypad 120 into the gauge housing 12 for connection with the CPU 17.Alternatively, the remote keypad 120 can be located on the handle 50.Because the handle 50 moves with the source rod 20, the power source tooperate the remote keypad 120 could be contained within the handle 50.For example, a battery can be provided or power can be established withsliding contacts between the gauge 10 and handle 50.

Further, the keypad 120, as stated above, can be an entity totallyseparate from the physical body of the gauge 10. For example, the remotekeypad 120 can be a fob that may be placed on a lanyard that can be hungaround the operator's neck. Methods of communication between the CPU 17in the gauge housing 12 and the remote keypad 120 for such embodimentswhere the remote keypad is secured to the handle or the remote keypad asa separate entity can be wireless in nature. For example, a transmittercan be located in the handle and a receiver can be located in the gaugehousing for embodiments where the remote keypad is located on thehandle. For embodiments where the remote keypad is a separate entitysuch as a fob, a transmitter can be located in the remote keypad and areceiver can be located in the gauge housing. Methods of wirelesscommunications can be established via infrared or RF, BLUETOOTH®, or thelike.

Methods of Configuration and Calibration

Described below are methods of calibration and configuration. Themethods of configuration and the methods of calibration set forth beloware provided by way of example to illustrate embodiments thereof and arenot meant to limit the present subject matter. Other methods ofconfiguration and the methods of calibration can be used withoutdeviating from the scope and spirit of the present subject matter.Further, these methods of configuration and methods of calibration canbe used on other embodiments of nuclear gauge other than those describedabove. For example, nuclear gauges similar in construction to thosedisclosed in U.S. Pat. Nos. 4,525,854, 4,701,868, 4,641,030, 6,310,936and 6,442,232 can use such methods of configuration and methods ofcalibration.

Configuration Methods

The same software and CPU can be used with different nuclear gauges.However, there are certain features on some nuclear gauges that are noton other nuclear gauges. In order to restrict access to customers whopurchase a nuclear gauge containing fewer features, the gauges must beconfigured at the factory. This configuration can be done by settingflags in permanent memory that are read by the gauge CPU.

Each of these flags can represent a gauge feature that is variable atmanufacturing time. These flags can set different settings for the gaugein which the software is employed. For example, the settings can relateto the source rod length, for example, whether the source rod is an8-inch unit, a 12-inch unit, or a unit for use on a backscatter onlygauge. The settings can relate to the indexing positions, for example,whether the indexing positions are at 1 inch or 2 inch increments. Suchsettings can also relate to the type and/or model of nuclear gauge, andwhether the gauge contains GPS capabilities or not. The owner'sidentification and contact information, serial number of the gauge andsources can also be stored for retrieval at any time by an authority.

To accomplish this configuration, a program can be written for acomputer, such as a personal computer, that allows an assembler toselect how the flags are set. This program can also communicate thisinformation to the gauge. These communications can be over the serialport. The assembler setting up the gauge flags can place the gauge in amode where the gauge is looking for specific commands from the serialport. Then, when the information entered into the program at thecomputer is correct, a computer command can be started that can takethis data and transfer it to the gauge over the serial port usingspecific commands. The gauge can set the appropriate flags in permanentmemory. When the software is executed, these flags can be checked todetermine gauge type, source rod and indexing information, and if GPScapabilities are available.

The nuclear gauge 190 that is configurable to operate in a plurality ofsettings can include a computing system 192. The computing system 192can be adapted to be configured to enable and to disable the settings ofthe nuclear gauge 190. A nuclear gauge configuration system 194 can bein communication via a communication connection 196 with the computingsystem 192 of the nuclear gauge 190. The communication connection 196can be a wired connection such as a cable connection between serialports or a wireless connection. At the nuclear gauge configurationsystem 194, commands can be communicated to the computing system 192 ofthe nuclear gauge 190 for one of enabling and disabling the settings ofthe nuclear gauge 190. The commands can be received by the nuclear gauge190 from the nuclear gauge configuration system 192. Once the commandsare received, the setting can be enabled or disabled based on thereceived commands. The commands can be created by user input at thenuclear gauge configuration system 194 that at least one of the settingsof the nuclear gauge 190 is to be enabled and disabled. As stated above,these settings of the nuclear gauge 190 can include a source rod length,indexing positions, gauge type, global positioning system (GPS)operability, calibration curve selection, calibration type, and ownerand serial number information.

In addition to the settings determined by the flags set forth above, thesettings that can be set using the configuration method can includeenabling or disabling diagnostic routines, service information andscheduling, USB port, automatic depth versus manual position detection,and a remote keypad.

Further, the settings that can be set using the configuration method caninclude the type of calibration that is used in a gauge. For example,the type of calibrations can be a method one calibration (one block), a5 block calibration, or a 3 block calibration. The calibration of suchgauges will be discussed in more detail below. Further, the gauge can beconfigured to operate with a nuclear gauge calibration device, such as aTroxler Tracker™ device provided by Troxler Electronic Laboratories,Inc., based in Research Triangle Park, North Carolina, for calibrating agauge or tracking gauge health. Such a nuclear gauge calibrating deviceis described in more detail in U.S. Pat. No. 6,369,381 and “The Manualof Operation and Instruction for the Model 6180 Troxler Tracker™Calibration Tracking System,” both of which are incorporated herein byreference in their entirety. The Manual of Operation and Instruction forthe Model 6180 Troxler Tracker™ Calibration Tracking System is providedby Troxler Electronic Laboratories, Inc., based in Research TrianglePark, North Carolina.

An exemplary use of the nuclear gauge calibrating device can be to useit to map a new or newly calibrated gauge response. The obtained datamay be stored in the gauge, so that enacting a menu would allow a userto make measurement at a later time on the device and compare resultswith previously stored data.

Also, an operator of a gauge can also select special calibration curvesor corrections for surface roughness or texture, chemical composition ofa mix or soils, soil composition, lithography of aggregate material, orcorrections for a mix design (e.g., aggregate size and distribution,asphalt content, and the like).

The options, or settings, are enabled and disabled via the softwareconfiguration. The options, once selected are reflected in a bit fieldmanipulated by the use of bit masks. Once the bit field is set, it isstored to non-volatile flash memory within the gauge.

A further example of a configuration method, generally designated 200,is illustrated in FIG. 28. A computer 202 is provided and is incommunication with a gauge 204. The configuration is started in step 206and the authentication key that permits access to the configurationprogram is validated in step 208. If the authentication key is invalid,then the configuration fails. If the authentication key is valid, thegauge type can be selected in step 210. For example, the gauge can be adensity gauge, a bulk density gauge, a thin overlay gauge, a thin layergauge or a combination thereof. In step 212, other options or featurescan be selected such as source rod length, indexing positions, andglobal positioning system (GPS) operability. Also, the options caninclude enabling diagnostic routines, service information andscheduling, USB port, automatic depth versus manual position detection,calibration curve selection, calibration type, and/or a remote keypad.In step 214, a serial number for the gauge can be entered. The commandline interface commands to be sent to the gauge can be encrypted usingan encryption key in step 216.

The computer 202 can then make contact with the gauge 204 to start aninterface in step 218. For example the computer 202 can send ahandshaking request to the nuclear gauge 204. As used herein,handshaking means an automated process of negotiation that dynamicallysets parameters of a communications channel established between twoentities before normal communication over the channel begins. It followsthe physical establishment of the channel and precedes normalinformation transfer. It is then determined in step 220 whether thegauge 204 has responded with an appropriate message within a set numberof tries which can be determined by the manufacturer or user. If not,then the configuration fails. If the gauge 204 does respond, then theencrypted command line interface (CLI) commands are sent to the gauge204 through a communication connection, such as an RS232, WIFI, or thelike. In step 224, encrypted information can be sent to the computer forconfirmation. A CLI program can be used for such function.

The commands from the computer 202 can now be received by the gauge 204.The CLI commands are decrypted with a local key in the gauge in step226. This key can be common to all gauges of a particular series orserial numbers or rely on a hardware key in the USB port such as adongle. The encryption scheme can be based either on symmetric keytechnique, an asymmetric technique such as public-private key technique,or a combination thereof. Moreover, the key can be associated with theauthentication scheme. Examples of encryption scheme include and are notlimited to Pretty Good Privacy (PGP®), gnu privacy guard, ElGamal, DSA,RSA, AES, 3DES, Blowfish, Twofish. The authentication scheme or keyenables the possibility to grant the ability to edit, read, and/or setall or a selection of option flags and related information. Depending onthe authentication information or key, the flags and data stored in thegauge may be edited or not, read or not. For example only certifiedcenters/users may be able to change the calibration constants and dates.

The commands are then converted in step 228. The section made on thecomputer are then stored on the gauge in the random access memory (RAM),or non volatile memory such as flash or E-PROM memory of the gauge instep 230. This verified stored configuration data is encrypted in step232 and sent back to the computer 202 from the gauge 204. In step 234,the computer 202 checks to see if the gauge's response is appropriate.If the response is not appropriate, then the configuration fails. If theresponse is appropriate, then the computer 202 can determine whether ornot the gauge 204 requests extended testing of the configuration in step236. If not, then the configuration ends successfully at 246. Ifextended testing is requested, then the computer 202 in step 238 sendsan encrypted test message using CLI to the gauge 204. The test messageis decrypted and the test is performed and results encrypted in step240. The encrypted information using the CLI in step 242 is sent back tothe computer 202 for confirmation. The encrypted message is checked bythe computer 202 to determine whether it is an appropriate response in244. If it is, then the configuration is successfully complete in 246.If the message is not appropriate, then the configuration fails.

Other similar configuration methods can also be performed between aconfiguration device such as a computer and the computing system of thenuclear gauge.

Calibration Methods

Normally, in nuclear gauges used to determine moisture and/or density ofthe materials, calibration has been completed by information gatheredand entered by the person attempting the calibration. Calibrationconstants needed for the operation of the gauge are calculated andmanually entered. Thus, there exists the great possibility thaterroneous contacts are entered, thereby leading to a greater opportunityof poor quality calibration that in turn can lead to false readings bythe nuclear gauges.

To increase the quality of calibration, the option to manually entercalibration constants manually can be eliminated. Calibration can beachieved through the use of a computer, such as a personal computer,containing software applications and a Command Line Interpreter (CLI)function located in the gauge. For example, the CLI can be a softwareapplication that is stored along with other software applications on thecomputing system of the gauge. Once the computer and gauge are incommunication with one another, through wireless or wiredcommunications, the computer can interrogate the computing system,including the memory, of a nuclear gauge for information needed tocalibrate the nuclear gauge. This information can include, for example,current index, counts, or the like. The computer can collect all of therelevant information and calculate calibration constants. Calibrationconstants can then be downloaded to the gauge via the CLI. Allcommunications between the gauge and the computer can be encrypted.

A method for calibrating a nuclear gauge 250 as shown in FIG. 29 caninclude providing a nuclear gauge 250 adapted to be remotely calibratedvia encrypted calibration communications. The nuclear gauge 250 caninclude a command line interpreter 252 adapted for receiving calibrationcommands. The command line interpreter 252 can be hardware or a softwareprogram that provides a command line interpreter function. A nucleargauge calibration system 256 in communication with the computing system254 of the nuclear gauge 250 can also be provided. The nuclear gaugecalibration system 256 can be connected to the computing system 254 ofthe gauge 250 by a communication connection 258. The communicationconnection 258 can be a wired connection or a wireless connection asdescribed above. The nuclear gauge calibration system 256 can be adaptedto interrogate the nuclear gauge 250 for calibration information. Thenuclear gauge calibration system 256 can communicate encrypted commandsto the nuclear gauge 250 for calibrating the nuclear gauge 250. Thecalibration information can include current index, counts, or like. Thecalibration information can also include gauge type, serial number ofgauge, serial number of sources, date, time, calibration constants,technician, calibration location, calibration type, type of materialbeing calibrated.

The calibration information from the nuclear gauge is communicated in anencrypted format to the nuclear gauge calibration system. The nucleargauge calibration system can then calculate calibration constants basedon the calibration information, and communicate the calibrationconstants to the nuclear gauge in an encrypted format. Allcommunications between the nuclear gauge and the nuclear gaugecalibration system can be encrypted.

For example, as shown in FIG. 30, a calibration method generallydesignated 260 can be provided. In step 262, the gauge can be placed inCLI mode and connected to the computer via a communication cable, suchas an RS232 cable. From a computer program on the computer, acalibration technician can select the source rod size and indexingintervals for the gauge to be calibrated in step 264. Further,calibration technician can select the type of calibration (3 block orusing a nuclear gauge calibration device, soil or asphalt), date, time,location, the duration of the count time, or the like. A “checkoff” file(structured random file format) can be created in step 266 based on thedata information selected by the technician. If a particular count orseries of counts is required, then the record in the file correspondingto that count or series of counts can be set to True; otherwise, it canbe set to False. In step 268, the calibration program in the computercan begin reading the checkoff file from a first record, and can readdown until a “True” record is encountered. Based on the location of this“True” record, the user in step 270 is prompted to place the gauge on aspecific block (or a poly standard block for the stat or drift test),place the source rod in a specific location and click a switch on thecomputer. In the event that no “True” record is found, then the datacollection process for the calibration is complete in step 272.

Based on the location of the current record in the checkoff file, thecomputer can create the specific command that the gauge needs toinitiate a count of a specific time duration in step 274. This commandcan be encrypted and then sent to the gauge through a communication portsuch as an RS232 port. The gauge can receive this encrypted command andcan un-encrypt it in step 276. The gauge then can take a count that hasthe count duration indicated in this un-encrypted command in step 278.When the gauge concludes the count that was initiated, the gauge cantake the results of the counts, create a text string, and encrypt thetext string in step 280. This text string can be sent by the gauge tothe computer via the communication port. The computer, which can beginwaiting for a reply from the gauge a few seconds before the count isscheduled to finish, can receive the encrypted data from the gauge andun-encrypts the data in step 282. The computer can write the unencrypteddata to a specific record location in a calibration data file in step284. The computer can change the content of the current record in thecheckoff file from “True” to “False” in step 286. In step 288, it can bedetermined if the current record was the last record in the checkofffile. If the current record in the checkoff file is the last record,then the data collection process for the calibration is complete. If thecurrent record in the checkoff file is not the last record, then theprogram goes back to step 268 and begins reading the checkoff file againto initiate the collection of more data.

As stated above, diagnostics of the health of the gauge that look atparameters such as the typical calibration constants, count rate,precision and slope as a function of density of each gauge, along withtheir standard deviations have in the past been performed only at thefactory. In the factory, external computer networks are wired to eachcalibration bay, the data is transferred by wire from the instrument tothe external computer, where computer programs known in the art are usedto curve fit, transfer the coefficients, store the coefficients to thegauge, and quality control check each measurement for deviations out ofthe standard expected values. The computing system of the gauge can havethe ability to perform all these external factory functions, yet notneed an external network to do so. The computing system of the gauge canaccomplish this by having increased functionality and the associatedcomputing power and memory needed to do it.

Generally, different methods of calibrating the density measurementsystem can be used including the method one calibration, the three-blockcalibration, or the five-block calibration. The three-block calibrationand the one block calibration are described in more detail below.Further, a method of calibrating the moisture measurement system canalso be used.

The calibration of a gauge is a combination of several independent setsof measurements and calculations. A separate calibration should beperformed at each source rod position (depth). Consequently, a completegauge density calibration can consist of up to twelve separate andindependent calibrations. Each source rod position of each gauge has itsown unique set of three density calibration constants. One of the maingoals of the calibration process is to determine the calibrationconstants for each source rod position for a given gauge. Ideally, agauge can be calibrated for the specific soil in which it is to be used.However, for typical construction soils, and for gamma rays, thedifferences in composition from one soil to the next are usually, butnot always, small. Therefore, gauges are calibrated using arepresentation of an “average” soil.

To avoid problems with soil standards, a combination of metallic blockscan be used as calibration standards. These blocks are homogenousthroughout, do not absorb significant amounts of moisture, retain theirphysical dimensions and surface integrity after repeated contact withgauges, and maintain their densities well. The materials that make upthese blocks are quite different from average soil. However, whencalibrating a gauge, mathematical adjustments are performed tocompensate for the differences in elemental composition between theblocks and average soil. These adjustments enable the blocks to “looklike” average soil.

Three-Block Calibration:

The Three-Block Calibration method has been accepted and implemented bythe American Society for Testing and Materials (ASTM) as ASTM standard:ASTM D7013-04, which is incorporated herein in its entirety. In theThree-Block Calibration, the gauge is placed on three standard blocks ofknown density: a magnesium block, an aluminum block, and a block made upof alternating sheets of magnesium and aluminum. For each standardblock, the density count is taken at each source rod depth. The countsfrom each block at each depth are then used to calculate the calibrationconstants for the gauge. The attenuation of gamma rays through amaterial is related to the count ratio, which is the ration between astandard count C_(std) and the measurement count C_(m). Here, for eachposition, the measurement count is attenuated through the material as afunction of its density as:C _(std) /C _(std) =Ae ^(−Bx) +C

Where:

-   -   X is the distance between the source and detectors;    -   B accounts for the material properties such as density and        chemical composition including where some photons are absorbed;        and    -   A and C relate to the geometry of the instrument.        In calibration, a measurement at a particular position such as 6        inches is performed at three densities, and thus 3 equations and        3 unknowns are used to solve for A, B, and C at each position.        These solutions are found by the usual methods such as the        method of least squares, or a direct curve fit using matrices        and determinants.        Method One Calibration:

A method one calibration is only used for established gauge models aftersufficient data has been collected for that gauge model and a group ofcoefficients can be determined that define a linear relationship betweenany two of the density counts obtained in a Three-Block Calibration forthat gauge model. A Method One Calibration uses only themagnesium/aluminum block to calculate the calibration constants. Adensity count is obtained at each source rod position. The density countand the coefficients for the gauge model are used to calculate thedensity counts for the magnesium and aluminum blocks. The results arethen used to determine the calibration constants for that source roddepth. In this method, only a single density measurement is obtained,and for each geometry a curve is defined assuming higher and lowerdensity count responses. Hence, at each position, a quality control stepmust be implemented where actual measurements on magnesium and aluminum(higher and lower densities) are physically checked. This method issimply a production time saver for calibration.

Moisture Calibration:

The calibration of the moisture measurement system includes threemeasurements: a moisture standard count and two other moistureresponses. These measurements are taken using the magnesium block (0%moisture) and a block made up of alternating sheets of magnesium andpolyethylene representing (moisture). Typically, the moisture value ofthe magnesium/polyethylene blocks used in such calibrations is between561 kg/m3 (35 pcf) and 625 kg/m3 (39 pcf).

After moisture counts have been taken on the magnesium andmagnesium/polyethylene blocks, the results are used to determine twomoisture calibration constants, as typically this is a linear equation.

Applying Calibration Constants:

After a gauge has been calibrated and its calibration constants havebeen determined, the constants are loaded into the gauge memory. Thegauge is then used to perform a series of quality assurance measurementsto verify the operation of the gauge. The gauge is used to measure anumber of blocks with known density and moisture values. On each block,a density measurement is taken at each source rod position. If the gaugereads the correct density value within 1 lbs./ft.³ (pcf), thecalibration for that source rod position is considered accurate. If themeasured density is incorrect, the density calibration for that sourcerod position is repeated.

Similarly, the gauge is used to measure the moisture on amagnesium/polyethylene block. If the gauge reads the correct moisturevalue within 1 pcf, the moisture calibration is considered accurate. Ifthe moisture measurement is incorrect, the moisture calibration isrepeated. When the gauge has passed all density calibration tests andthe moisture calibration tests, it is ready to be shipped.

The calibration blocks used to calibrate such gauges can be calibratedusing NIST-traceable standards. The gravimetric densities of theseblocks are found using the dimensions and mass of each calibrationblock. These blocks are referred to as the Primary Calibration StandardBlocks. The complete set of primary blocks can be used to perform ahigh-precision Three-Block Calibration and calibration confirmation on agauge. This gauge is then referred to as a master gauge and is used toquickly measure a traceable density of other calibration blocks withoutthe tedious dimensional and mass measurements.

The computing system of the gauge through embedded software canfacilitate the performance of a calibration method 300 as shown in FIG.31. A calibration routine can be entered in step 302. A technicianworking with the nuclear gauge to carry out the calibration can beprompted to obtain a standard count in step 304. This prompt can takeplace on the LCD screen on the user interface of the gauge. In step 306,the technician is prompted, for example, through the LCD screen, toplace the gauge on the first (magnesium block) and adjust the source rodto a backscatter, or the first position. At step 308, the gaugeautomatically notes and detects that the source is in backscatterposition, and adjusts the counting time accordingly. The program canthen prompt the technician in step 310 to hit the “start” switch,whereby the gauge obtains a count, and stores this value in itscomputing system memory.

At the conclusion of the count in step 312, the program can prompt thetechnician to place the source in a second position. Upon the activationof the “start” switch for a second count, the gauge can automaticallyselect the time for the measurement at this second position. The gaugeobtains a count at this second position, and stores this value in itscomputing system memory. In step 316, it can be determined whether allthe counts for the specified block are complete. If not, the steps 312through 314 can be repeated until all the counts within this firstdensity block are completed and all counts have been recorded in thegauge. If all the counts for the first density block are collected andstored, it can be determined if all the counts for the other densityblocks have been taken in step 318. If not, the technician can then beprompted to move the gauge to the next density block and the steps 306through 316 can be repeated. At the end of taking all densitymeasurements and desired positions, the gauge can perform its owncalibration calculating the A, the B, and the C's for each position thusestablishing the calibration curves for each desired position in step320. The gauge then can perform a quality control routine in step 322.

As shown in FIG. 32, the computing system can also carry out the qualitycontrol routine 322. The quality control routine can use factoryinformation stored inside the gauge to perform diagnostics such asanalyzing the coefficients of each curve for slope, count rate,precision and standard deviation in step 324. In particular, thisfactory information is standard information that can be downloadedbefore the nuclear gauge is used or before the information is needed.Thus, this previously downloaded standard information can be useful inperform diagnostics on the gauge. Provided that all diagnostics are ingood order, the gauge in step 326 can then prompt the technician toplace the gauge on a certain density standard. Once the gauge isproperly placed, the gauge can prompt the technician to begin a qualitycontrol count in step 328. At this point in step 330, the gauge cancompare the actual density measured by the gauge at this position to theexpected value stored in the gauge. In step 332, the gauge can thendecide whether the measurement passes or fails. In the step 334, it canbe determined if all the positions are checked. If not, the techniciancan be asked to move the gauge to the next position. If all thepositions are checked, a full report can be displayed by the gauge onthe LCD screen, printed to paper, or stored in a portable USB memory fortransfer to a host computer in step 336. This full report suggests whichpositions should be recalibrated, or if a possible problem might existin the mechanical or electrical components of the gauge.

This internal calibration capability can reduce the cost of muchequipment needed for calibration, not to mention the frustratinginterconnect problems and data transfer that is associated with currentmethods. The internal calibration capability can provide economical,frustration-free calibration, quality control and diagnostics not onlyfor factory technicians but for interested users that have thecapability and traceable standards necessary for calibration. Users canpurchase the rights to access the embedded program, perform their owncalibrations, and transfer the results to an external memory or computerdevice, if desired. Users can also, via the internet, send their resultsto the factory for further analysis or storage.

Gauge Calibration Performed Internally by Gauge Base on InformationProvided by a Nuclear Gauge Calibrating Device:

Although this description incorporates the use of one or more heavy,non-portable calibration blocks, there is an alternative for fieldanalysis and calibration using simulated scaled down calibrationstandards such as the multipoint nuclear gauge calibrating device or asingle point device, both of which are described in U.S. Pat. No.6,369,381.

Note that the density values from a nuclear gauge calibrating device,such as the device sold under the name TRACKER™ by Troxler ElectronicLaboratories, Inc. of Research Triangle Park, North Carolina, can alsobe stored in the memory of the computing system of the gauge. Also, theself-calibration described above can be accomplished using a fieldcalibration/verification device instead of the multiple metal blocksdescribed above.

Typically, to confirm the density calibration of the gauge at a givendepth the confirmation program that is stored and can be executed in thecomputing system of the gauge can be entered. The gauge can prompt theuser, for example, through the LCD screen to do the following:

-   -   1. Place the gauge on the nuclear gauge calibrating device.    -   2. Set the source rod to the depth suggested by the program on        the gauge and displayed on the LCD screen of the gauge.    -   3. Select the desired index wheel position on the nuclear gauge        calibration device from a calibration sheet, such as a TRACKER®        Calibration Sheet provided by Troxler Electronics Laboratories,        inc., located in Research Triangle Park, North Carolina, and        move the index wheel to the selected position. The index wheel        should click into the detent for the selected position. The        index wheel can be a circular disc on the nuclear gauge        calibration device that has 5 detented positions where the user        looks up the source rod position and finds 3 positions (from the        5 offered) that give low, medium and high density simulations.        The index wheel can be physically spun to the required density.        Alternatively, an automated index wheel can have a stepping        motor on it. Here, the calibration routine automatically gets        the three densities for each source rod position, then prompts        for the technician to move the rod to the next position.    -   4. At the gauge, set the recommended count time and obtain a        density measurement.    -   5. Compare the measured density to the density stored in the        calibration sheet residing in the memory of the gauge for the        selected depth and index wheel position using the internal        program of the gauge. If the measured density is within ±2 pcf        of the value listed on the calibration sheet, the gauge        calibration for that depth and that density can be acknowledged        as accepted, accurate or a pass. If the difference between the        measured density and the listed value is greater than 2 pcf, the        internal software of the gauge can repeat step 4 using a longer        count time. If the difference between the measured and listed        densities is still greater than 2 pcf, the output of the gauge        will suggest and note that this position should be recalibrated.

To confirm the moisture calibration of the gauge, the software can checkthe moisture measurement on the moisture standard of the nuclear gaugecalibrating device. Here, the gauge can select a count time, ask theuser to place the gauge on the nuclear gauge calibrating device, andselect the “start” switch. At the conclusion of the count, the gauge cancompare the measured moisture to the moisture calibration value shown onnuclear gauge calibrating device calibration sheet stored in gaugememory. If the measured moisture is within ±2 pcf of the value listed onthe calibration sheet, the gauge moisture calibration is accepted asaccurate. If the difference between the measured moisture and the listedvalue is greater than 2 pcf, another moisture measurement can be taken,preferably using a longer count time. If the difference between themeasured and listed values is still greater than 2 pcf, the gauge cansuggest that it should be placed in the calibration mode andrecalibrated.

Gauge tracking is a powerful method of monitoring changes in theresponse of a gauge. A packet of density and moisture tracking chartscan be supplied with each nuclear gauge calibrating device for manualobservations. These charts can be used to record the results of theconfirmation measurements performed on a gauge. Any changes in gaugeresponse over time will be reflected on the tracking charts. Conversely,with the processor and memory contained on the gauge, these charts canbe stored, manipulated, and monitored by the gauge itself.

With each nuclear gauge calibrating device, comes an assignment ofdensities found using a master gauge, which can be created as describedabove. Since the density assignments are made with a second mastergauge, and not the particular production gauge that a customer owns, thedensity values of the nuclear gauge calibrating device can be slightlydifferent than what a perfectly calibrated production gauge would read.This statistical variation is the result of the energy response of eachgauge, coupled with any geometrical differences between gauges, and thefinite volume of a simulated calibration device like the TRACKER®.

To overcome tracking errors, which can be up to 5 pcf, the softwarestored on the computing system of the gauge can have the ability toassign its own densities to the nuclear gauge calibrating device. Hence,the nuclear gauge calibrating device and matched gauge will generallyread the same, or within a few tenths of a pcf, for example, betweenabout 0.05 pcf to about 0.5 pcf. To enable this feature, the user canenter the “define tracking values” menu of the gauge, and follow theinstructions by the gauge as displayed on the LCD screen.

For example, the gauge can prompt the user to input the serial number ofthe nuclear gauge calibrating device, the user name and gauge serialnumber. The gauge can prompt the user to place the gauge on the nucleargauge calibrating device and put the source rod at a specified depth.Further, the gauge can prompt the user to place the index wheel ordensity of the nuclear gauge calibrating device at the proper positionfor that gauge model and depth. The gauge can then select a countingtime and ask the user to start the measurement. At the end of themeasurement, the gauge can store the density of the nuclear gaugecalibrating device in its memory, and ask the user to place the sourcerod and nuclear gauge calibrating device density at the next position.At the conclusion of all desired source rod and density positions, aninternal memory map of the values from the particular nuclear gaugecalibrating device, and particular gauge can be stored in the gauge.Conversely, instead of exact density values, corrections to the densityvalues supplied by the factory can be stored. Note that this new tableof densities is not a general assignment like the factory values, but isparticular for this exact gauge serial number for which the tests wererun.

This internal map can be used for future diagnostics or “tracking” ofthis particular gauge. In later tracking use, the technician can enterthe serial number of the nuclear gauge calibrating device, and the gaugewould check this number with that stored serial number which defined thetracking density map. If these serial numbers agree, the gauge canprompt the technician to place the gauge on the nuclear gaugecalibrating device, and begin measurements. These measurements can bestored at future dates, and an actual graph of the calibratingdevice-gauge matched results measured against time can be produced as anoutput of the gauge.

For example, if the technician has a daily assignment to measure thesoil density and moisture at 6 inches on-site, he can call up theconformation or tracking program internal to the gauge, select the6-inch position on the keypad, place the unit on the nuclear gaugecalibrating device, input the nuclear gauge calibrating device serialnumber and press a “start” switch. The gauge can select the countingtime and commence a measurement. The gauge can then compare thismeasurement to the value that the gauge gave in its history, and canconfirm the quality of the calibration.

For tracking purposes, a density tracking chart 400 as shown in FIG. 33can be used. The Y-axis of each grid is incremented in units of 1 pcfabove and below the density calibration value represented by thecenterlines 401. The solid lines 402, 404 on each grid represent theupper and lower acceptable density values, respectively. In thisexample, these limit lines 402, 404, are defined as the listed densitycalibration value±2 pcf. For example, in the upper grid, the centerline401 represents 110.4 pcf. The upper limit line 402, therefore,represents a value of approximately 112.4 pcf and the lower limit line404 represents a value of approximately 108.4 pcf.

The gauge can also record the measurement date including the month inspaces 406, the day in spaces 408, and year in spaces 410 for thedensity tracking chart 400. The gauge can instruct the user to perform adensity calibration confirmation at the different index wheel positions.The gauge can plot each measured value on the appropriate grid. Thegauge can also record whether the confirmation passed (P) or failed (F)in the spaces 412 provided at the bottom of the chart. Such a densitytracking chart 400 can be displayed by the LCD screen on the gauge,printed or stored on the USB for transfer to another medium.

FIG. 34 shows a sample moisture tracking chart 430 that can be displayedby the LCD screen of the gauge as well. The chart 430 is used tointernally log the moisture calibration measurements, which are notdependent upon the source rod depth. The centerline 431 can representthe moisture calibration value. As with the density tracking chart 400,the Y-axis is incremented in units of 1 pcf above and below thecenterline 431 that represents the moisture calibration value. The solidlines 432, 434 on the grid represent the upper and lower acceptablemoisture values, respectively upper and lower acceptable moisture valuesrepresented by the solid lines 432, 434 are defined as the listedmoisture calibration value±1 pcf. For example, as described above, thecenterline 431 represents 7.8 pcf. The upper limit represented by solidline 432, therefore, is 8.8 pcf and the lower limit represented by solidline 434 is 6.8 pcf. As with the density tracking chart 400, the gaugewill record the measurement date the measurement date including themonth in spaces 436, the day in spaces 438, and year in spaces 440 forthe moisture tracking chart 430. Through its software, the gauge caninstruct the user, for example on the LCD screen to perform a moisturecalibration confirmation. The gauge can plot each measured value on theappropriate grid. The gauge can also record whether the confirmationpassed (P) or failed (F) in the spaces 442 provided at the bottom of themoisture tracking chart 430.

As a general rule, when reviewing the density and moisture trackingcharts, 95% of the data points on the tracking chart should fall withinthe upper and lower limit lines. If a data point falls outside thelimits, and remains outside the limits during repeated tests, the gaugeresponse has changed and the gauge should be recalibrated.

Embodiments of the present disclosure shown in the drawings anddescribed above are exemplary of numerous embodiments that can be madewithin the scope of the appending claims. It is contemplated that theconfigurations of nuclear gauges and the methods of configuration andcalibration of the same can comprise numerous configurations other thanthose specifically disclosed. The scope of a patent issuing from thisdisclosure will be defined by these appending claims.

What is claimed is:
 1. A method for calibrating a nuclear gauge having asource, the method comprising: providing a nuclear gauge comprising aradiation source, the radiation source being coupled with a computingsystem with a machine readable program stored thereon containing acalibration routine; wherein an operator places the gauge on one or morespecified blocks to adjust the source within each of the one or morespecified blocks to one or more specified positions to initiate ameasurement; determining, by the operator or computing system, that thesource is at each of the one or more specified positions before eachmeasurement begins; selecting or verifying, by the operator or computingsystem, measurement times before each measurement begins based on eachof the one or more specified positions of the source to obtaincalibration information; obtaining measurements at each of the one ormore specified positions; storing the measurements within the computingsystem of the nuclear gauge; and calculating, by the nuclear gauge, foreach of the one or more specified positions, calibration coefficients.2. The method of claim 1, wherein at least one position in each block isone of a backscatter position and transmission position.
 3. The methodof claim 1, wherein at least one block of the one or more specifiedblocks is a magnesium, aluminum, granite, limestone, poly, ormagnesium-aluminum block.
 4. The method of claim 3, wherein the one ormore specified blocks comprise one to five blocks.
 5. The method ofclaim 1, wherein at least one block of the specified calibration blockis a composite containing at least one of cadmium, lead, tungsten,magnesium, aluminum, granite, limestone, poly configured to representone or more densities of a single block.
 6. The method of claim 5,wherein the one or more specified blocks comprise one to five blocks. 7.The method of claim 6, further comprising repeating the steps ofdetermining that the source is at each of the one or more specifiedpositions, selecting or verifying the measurement times, obtainingmeasurements and storing the measurement results within the computingsystem of the nuclear gauge for measurement positions of the sourcewithin multiple blocks.
 8. The method of claim 1, wherein selecting themeasurement times comprises automatically selecting the measurementtimes.
 9. The method of claim 1, further comprising, at the nucleargauge, performing a quality control routine on the gauge to confirmcalibration.
 10. The method of claim 1, wherein the quality controlroutine comprises using previously measured results stored in thecomputing system of the gauge to perform diagnostics on the gauge.